1. Field of Invention
The present invention relates to a piezoelectric device including a piezoelectric vibrating reed contained in a package, and to an enhancement in a method of sealing the packages.
2. Description of Related Art
Small information apparatuses, such as HDDs (hard disk drives), mobile computers, and IC cards, and electronic apparatuses, such as cellular phones and the like, use a piezoelectric device, such as a piezoelectric vibrator, a piezoelectric oscillator, or the like, which includes a piezoelectric vibrating reed contained and sealed in a package.
Such a piezoelectric device is formed by setting a piezoelectric vibrating reed in a ceramic package having the open top, and fixing a cover to the package to seal the package.
The piezoelectric device is manufactured as schematically shown in a flow chart of FIG. 28.
First, a box-like package including a piezoelectric material, such as ceramic or the like, is prepared, and a piezoelectric vibrating reed including a piezoelectric material, such as quartz or the like, is fixed to an electrode, which is previously formed in the package, with a conductive adhesive (ST1).
Next, the package is sealed with a cover using a brazing material (hereinafter “cover sealing”) (ST2). Then, the package is annealed by external heating to discharge, for example, harmful gas components produced from the conductive adhesive used to fix the piezoelectric vibrating reed (ST3).
Furthermore, the annealed package is placed in vacuum to remove the gas components to the vacuum from a through hole previously formed in the package, and then the through hole is filled with a metal material under heating to seal the through hole in vacuum (hereinafter “hole sealing”) (ST4).
Finally, a laser beam is transmitted through the cover from the outside to irradiate the electrode of the piezoelectric vibrating reed contained in the package, to partially evaporate the electrode. In this way, the frequency is controlled in a mass reduction system to control the vibration frequency (ST5), and then necessary inspections are performed to complete the piezoelectric device.
In the step ST2, the package is sealed with the cover by using, for example, such a belt furnace-type sealing apparatus 1 as shown in FIGS. 29(a) and 29(b). FIG. 29(a) is a schematic plan view of the sealing apparatus 1, and FIG. 29(b) is a schematic side view of the sealing apparatus 1.
The sealing apparatus 1 includes a heating chamber 2 in which a belt 4 including a conveyor belt is moved. Also, a plurality of heaters 3 is disposed along the movement direction of the belt 4 in the heating chamber 2. Furthermore, a package 6 is placed on the belt 4 and moved by the belt 4 along the direction of an arrow A. In the heating chamber 2, the package 6 is heated by the heaters 3 provided above the belt 4 during movement.
As shown in an enlarged view of FIG. 30, the package 6 is arranged on the belt 4 with the bottom facing upward and a cover 7 facing downward. On the open side of the package 6, a brazing material 8 including lead-containing low-melting-point glass, Au/Sn, or the like is disposed between the package 6 and the cover 7. This structure is disclosed in columns 0003 and 0011 of Japanese Unexamined Patent Application Publication No. 8-78955, for example.
A piezoelectric vibrating reed 6a is contained in the inner space S of the package 6. As described above with respect to ST1 shown in FIG. 28, the piezoelectric vibrating reed 6a is fixed to the inner bottom of the package 6 with a conductive adhesive 6b including a silver paste or the like.
In this state, a tray 3 and the package 6 are moved in the direction shown by arrow A in FIGS. 29(a) and 29(b) so that the package 6 is sealed with the cover 7 during the passage through the heating chamber 2.
Namely, as shown in FIGS. 29(a) and 29(b), the tray 3 and the package 6 are moved in the direction shown by arrow A in FIGS. 29(a) and 29(b), and the brazing material 8 between the package 6 and the cover 7 is melted during the passage through the heating chamber 2 to seal the package 6 with the cover 7.